Your mission in this bloody zombie killing online game is to blast as many zombies as you can before they get you. The game features varying zombie types, each with their own strengths and weaknesses. You earn money for each zombie you put down. You can use your hard earned money between rounds to purchase more than 20 different weapons

These are your legs W, A, S, D to move them.
Now you have a torso, which is handy for zombie killing.
Point and Click using the mouse to unload a round in that direction. With automatic weapons you can hold down the grigger.
Hold you it was easy.
Your hud shows you what weapon you are using and will show when you're beginning to run out of ammo.
Press R to reload.
Your hud also shows the amount of health and money you have.
It also allows you to select weapons from those available.
Weapons can be bought from the menu between rounds.
Kill zombies, earn money, buy bigger guns, kill more zombies, simple!
Good luck